diff --git a/include/lspserv.h b/include/lspserv.h
index 286c75b6c..d4b22dbda 100644
--- a/include/lspserv.h
+++ b/include/lspserv.h
@@ -175,6 +175,8 @@ namespace AsymptoteLsp
     unique_ptr<SymContextFilemap> symmapContextsPtr;
     unique_ptr<unordered_map<std::string, std::vector<std::string>>> fileContentsPtr;
     std::string plainFile;
+
+    std::mutex onChangeMutex;
   };
 
   class TCPAsymptoteLSPServer : public lsp::TcpServer, public AsymptoteLspServer
diff --git a/src/lspserv.cc b/src/lspserv.cc
index 328cf9e47..df3aa11ac 100644
--- a/src/lspserv.cc
+++ b/src/lspserv.cc
@@ -317,6 +317,7 @@ std::string wslUnix2Dos(std::string const& unixPath)
 
   void AsymptoteLspServer::onChange(Notify_TextDocumentDidChange::notify& notify)
   {
+    std::lock_guard lk(onChangeMutex);
     logInfo("text change notification");
 
     auto& fileChange = notify.params.contentChanges;